sbcl.sbcl/contrib/sb-rotate-byte

This module provides an implementation of ROTATE-BYTE, described at
<http://www.cliki.net/ROTATE-BYTE">.  Its inclusion is hoped to
achieve two aims:

(1) to provide the necessary functionality for implementations of
    cryptographic and hashing algorithms (e.g. MD5);

(2) to provide an example of the things that can be achieved by using
    the external but unsupported interfaces to the compiler.

Included in the module as of 2003-02-11 is an efficient implementation
of unsigned 32-bit rotation for the x86; when the compiler can prove
that the rotation in question is of an (UNSIGNED-BYTE 32) over the
byte specifier (BYTE 32 0), it will compile directly to machine
rotation instructions.  Patches for similar functionality on other
platforms are welcome.